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<a name="AVR-Built_002din-Functions"></a>
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<p>
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<a name="AVR-Built_002din-Functions-1"></a>
<h4 class="subsection">6.60.10 AVR Built-in Functions</h4>

<p>For each built-in function for AVR, there is an equally named,
uppercase built-in macro defined. That way users can easily query if
or if not a specific built-in is implemented or not. For example, if
<code>__builtin_avr_nop</code> is available the macro
<code>__BUILTIN_AVR_NOP</code> is defined to <code>1</code> and undefined otherwise.
</p>
<dl compact="compact">
<dt><code>void __builtin_avr_nop (void)</code></dt>
<dt><code>void __builtin_avr_sei (void)</code></dt>
<dt><code>void __builtin_avr_cli (void)</code></dt>
<dt><code>void __builtin_avr_sleep (void)</code></dt>
<dt><code>void __builtin_avr_wdr (void)</code></dt>
<dt><code>unsigned char __builtin_avr_swap (unsigned char)</code></dt>
<dt><code>unsigned int __builtin_avr_fmul (unsigned char, unsigned char)</code></dt>
<dt><code>int __builtin_avr_fmuls (char, char)</code></dt>
<dt><code>int __builtin_avr_fmulsu (char, unsigned char)</code></dt>
<dd><p>These built-in functions map to the respective machine
instruction, i.e. <code>nop</code>, <code>sei</code>, <code>cli</code>, <code>sleep</code>,
<code>wdr</code>, <code>swap</code>, <code>fmul</code>, <code>fmuls</code>
resp. <code>fmulsu</code>. The three <code>fmul*</code> built-ins are implemented
as library call if no hardware multiplier is available.
</p>
</dd>
<dt><code>void __builtin_avr_delay_cycles (unsigned long ticks)</code></dt>
<dd><p>Delay execution for <var>ticks</var> cycles. Note that this
built-in does not take into account the effect of interrupts that
might increase delay time. <var>ticks</var> must be a compile-time
integer constant; delays with a variable number of cycles are not supported.
</p>
</dd>
<dt><code>char __builtin_avr_flash_segment (const __memx void*)</code></dt>
<dd><p>This built-in takes a byte address to the 24-bit
<a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">address space</a> <code>__memx</code> and returns
the number of the flash segment (the 64 KiB chunk) where the address
points to.  Counting starts at <code>0</code>.
If the address does not point to flash memory, return <code>-1</code>.
</p>
</dd>
<dt><code>uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)</code></dt>
<dd><p>Insert bits from <var>bits</var> into <var>val</var> and return the resulting
value. The nibbles of <var>map</var> determine how the insertion is
performed: Let <var>X</var> be the <var>n</var>-th nibble of <var>map</var>
</p><ol>
<li> If <var>X</var> is <code>0xf</code>,
then the <var>n</var>-th bit of <var>val</var> is returned unaltered.

</li><li> If X is in the range 0&hellip;7,
then the <var>n</var>-th result bit is set to the <var>X</var>-th bit of <var>bits</var>

</li><li> If X is in the range 8&hellip;<code>0xe</code>,
then the <var>n</var>-th result bit is undefined.
</li></ol>

<p>One typical use case for this built-in is adjusting input and
output values to non-contiguous port layouts. Some examples:
</p>
<div class="smallexample">
<pre class="smallexample">// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0)
</pre></div>

</dd>
<dt><code>void __builtin_avr_nops (unsigned count)</code></dt>
<dd><p>Insert <var>count</var> <code>NOP</code> instructions.
The number of instructions must be a compile-time integer constant.
</p>
</dd>
</dl>

<p>There are many more AVR-specific built-in functions that are used to
implement the ISO/IEC TR 18037 &ldquo;Embedded C&rdquo; fixed-point functions of
section 7.18a.6.  You don&rsquo;t need to use these built-ins directly.
Instead, use the declarations as supplied by the <code>stdfix.h</code> header
with GNU-C99:
</p>
<div class="smallexample">
<pre class="smallexample">#include &lt;stdfix.h&gt;

// Re-interpret the bit representation of unsigned 16-bit
// integer <var>uval</var> as Q-format 0.16 value.
unsigned fract get_bits (uint_ur_t uval)
{
    return urbits (uval);
}
</pre></div>

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